docs: def sitecol(self):
          """
          Read the site collection from .filename and cache it
          """
          if 'sitecol' in vars(self):
              return self.__dict__['sitecol']
          if self.filename is None or not os.path.exists(self.filename):
              # case of nofilter/None sitecol
              return
          with hdf5.File(self.filename, 'r') as h5:
              self.__dict__['sitecol'] = sc = h5.get('sitecol')
          return sc